Summary of tests with DDT in 1944 for control of forest insects


Material Information

Summary of tests with DDT in 1944 for control of forest insects
Physical Description:
7 p. : ; 27 cm.
Craighead, Frank C ( Frank Cooper ), 1890-1982
Brown, R. C
United States -- Bureau of Entomology and Plant Quarantine
United States Department of Agriculture, Agricultural Research Administration, Bureau of Entomology and Plant Quarantine
Place of Publication:
Washington, D.C
Publication Date:


Subjects / Keywords:
Insecticides -- Testing   ( lcsh )
Insect pests -- Control   ( lcsh )
Forest insects -- Control   ( lcsh )
federal government publication   ( marcgt )
non-fiction   ( marcgt )


General Note:
Caption title.
General Note:
At head of title: United States Department of Agriculture. Agricultural Research Administration. Bureau of Entomology and Plant Quarantine.
General Note:
General Note:
"April 1945."
General Note:
Reproduced from a typescript.
Statement of Responsibility:
compiled by F. C. Craighead and R. C. Brown, Division of Forest Insect Investigations.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 030289953
oclc - 659498955
System ID:

Full Text

April 1945 E-649

United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine


Compiled by F. C. Craighead and R. C. Brown, Division of Forest
Insect Investigations

During the past year DDT has been tested on an experimental scale
for the control of a number of forest insects. These experiments indi-
cate that no development in the last 25 years has offered so much prom-
ise for the control of many forest insects, particularly defoliators.
Judging from these experiments, DDT is far more effective in low concen-
trations than any other commercial insecticide. Because of the small
amount required per acre, it is especially well suited to application
from airplanes, and indications are that it may make possible the pro-
tection of extensive areas of valuable timberland. The remarkable
residual qualities of the DDT deposit make it particularly well adapted
for the control of certain species. Its toxic effect, however, on
beneficial insects, fish, and wildlife in the forest is a problem which
will require thorough investigation, and such investigations are under-
way in cooperation with the Fish and Wildlife Service, U. S. Department
of the Interior, and other agencies.

The material presented here is summarized from reports on experi-
ments conducted at several field laboratories of the Division of Forest
Insect Investigations, as indicated. The more detailed results of these
investigations are being published under authorship of the workers who
conducted the studies.

DDT has been tested against defoliators, bark beetles, wood borers,
termites, and a number of sucking insects. It has been applied in the
form of suspensions, solutions, and emulsions, by means of airplanes,
high-powered sprayers, knapsack sprayers, and hand atomizers. Early
experiments with forest insects indicated that DIT mixed with ground
pyrophyllite and applied as a dust was effective in only a few specific
cases. With DOT suspensions there was considerable survival among the
insects tested. Consequently, most of the experimental work has been
conducted with solutions and emulsions.

A large number of solvents and emulsifying agents have been used in
developing the various spray formulas that have been tested and further
work along this line is underway.

AY 4- 194S


Aerial Application of DDT

Experiments in the aerial application of DDT were conducted co-
operatively by P. B. Dowden of the New Haven, Conn., laboratory of the
Division of Forest Insect Investigations, and. D. Whittam of the Division
of Gypsy and Brown-Tail Moths Control, Greenfield, Mass. These appli-
cations were for the control of the gypsy moth (Porthetria dispar (L.)),
the green-striped maple worm (Anisota rubicunda (F.)), the red-headed
pine sawfly (eodiprion lecontei (Fitch)), and the spruce budvorm
(Archips fumiferana (Clem.)). Complete control of the gypsy moth was
obtained in a 20-acre oak woodland with 5 pounds of DDT in 5 gallons
of solvent per acre, applied before the eggs had hatched and before the
foliage appeared. Later tests with the same dosage killed all the second-
and third-stage larvae of the gypsy moth in a 5-acre woodland plot. The
spray formula used in these tests consisted of 1 part by weight of DIDT,
1 part of cyclohexanone or 1.5 parts of xylene, and 7 parts of a light
oil. A similar formula was used in nearly all subsequent tests, except
that from 1.5 to 1.8 parts of xylene was substituted for 1 part of
cyclohexanone as a DDT solvent. The spray settle. through the forest
canopy to the understory as a fine mist, leaving, upon evaporation of
the liquid, a uniform crystalline deposit of DDT on all parts of the

Complete control of the green-striped maple worm was obtained with
the same dosage in a Vermont maple-sugar orchard.

Complete control of the red-headed pine sawfly in a red pine plant-
ation in northern New York was obtained by applying 2j pounds of DYDT
per acre. On the fringes of this sprayed area, where the spray drifted,
complete control wai obtained with a dosage believed to be not more than
1 pound of DDT in 1 gallon of liquid per acre.

The results of aerial tests in Canada against the spruce budworm
cannot be evaluated until 1945. However, tests with high-powered ground
equipment, conducted at the Fort Collins, Colo., laboratory by L. W.
Orr and N. D. Wygant, demonstrated that the spruce budworm can be con-
trolled with dosaeea as low as 2.5 pounds of DDT per acre, applied as
an emulsion in linseed oil or as a finely divided alcohol-water suspen-
sion. Some of the sprays were applied prior to larval activity in the
spring; others were used when the larvae were one-half to full grown.
There were indications that the early applications, which killed the
young larvae as they began feeding, were partially effective in killing
the moths several weeks later; therefore, one treatment may result in
control of two generations of some species of insects.

Because of the success obtained with these lower dosages during
the spring and summer of 1944, an extensive series of aerial tests were
made during September to determine the results from further reduction

of dosage. The observations indicated that the gallonage of spray
per acre must be varied according to the volume or area of foliage
to be treated. Tentatively, it appears that, where there is rela-
tively little foliage, as in plantations, good control may be ex-
pected from 1 pound of DDT in 1 gallon of liquid per acre, whereas
under forest conditions possibly twice that amount may be required.
In the control of many forest insects, however, a complete kill may
not be necessary to obtain the desired objective. In many cases pre-
venting defoliation to an extent that will enable the trees to survive
will be sufficient. Coverage, therefore, need not be complete and
perfect lapping of the swaths is not necessary. It may be possible to
use considerably lower dosages to accomplish this objective. Further
development of distributing equipment and the use of larger planes
may eventually make it possible to treat several hundred acres of
woodland with one load of insecticide.

Effect of DDT on Water and Wildlife

A 40-acre wooded watershed surrounding a 3-acre reservoir in
Pittston, Pa., was treated by airplane with 5 pounds of DDT in 5 gal-
lons of liquid per acre, for the purpose of determining the amount of
DDT present in the reservoir after rain. The area was treated on
August 14, and by August 17 three-fourths of an inch of rain had fallen.
Water samples were taken from the reservoir and from the tap of a
factory nearby. Chemical analysis of these samples made by the Division
of Insecticide Investigations showed that each sample contained less
than 1 part of DDT per 100 million parts of water. Such small amounts,
in the opinion of the Food and Drug Administration, Federal Security
Agency, could result in no health hazard from consumption of the water.

A study of the watershed area and the reservoir was made by P. B.
Dowden of the Division of Forest Insect Investigations, H. K. Townes
of the Division of Insect Identification, and N. Hotchkiss of the Fish
and Wildlife Service, to determine the effect of DYDT on the fauna of the
forest and the reservoir. Briefly it may be stated that the application
of DYDT severely reduced the abundance of most insects present in the
forest, but for the majority of species a sufficient number were left
to repopulate the area. Sufficient spray drifted on to the reservoir
to cover the surface of the water with a light film of oil. Within
a few hours this oil film was blown by the wind to one end of the re-
servoir. There waa a high mortality of adults of a number of species
of aquatic insects which were on or near the surface of the pond. Some
mortality of immature stages of insects at the surface of the water was
noted. The insects living on the bottom of the reservoir seemed to be
unaffected by this treatment.

There was no indication of mortality among the bird life of the
forest, but owing to the mobility of the bird population at the time
of the spraying it cannot be concluded that there was no effect. The
only effect noted on other vertebrates was on the day following treat-
ment, when a number of leopard frogs and bullfrogs and a few sunfishes
and minnows were dead or seriously affected. Unfortunately time did
not permit a careful study of this area except for a few days subsequent
to treatment. However, general observations on the 20-acre gypsy moth
plot sprayed early in the spring indicated that the fauna were back to
normal in 10 or 12 weeks. It was generally concluded that a thorough
ecological investigation of the effect of DIDT on the fauna of forests,
lakes, and streams should be undertaken before recommendations are made
for the treatment of extensive forested areas.

Wood Borers and Termites

Preliminary work with DDT by R. A. St. George, at Beltsville, Md.,
H. R. Johnston, at Saucier, Miss., and R. C. Hall,at Berkeley, Calif.,
indicates that it may be an effective insecticide for use on valuable
logs to prevent the attack of bark beetles, ambrosia beetles, and wood
borers. Protection lasting 2 months was obtained with 2- to 10-percent
solutions in diesel oil or kerosene. Wood borers such as Monochamus
and Acanthocinus were more easily killed or repelled than bark beetles
and particularly ambrosia beetles. The latter require concentrations co
at least 5 percent. Tests in Mississippi were less effective than those
at Beltsville, the great difference in rainfall probably being an im-
portant factor.

Preliminary work by C. H. Hoffmann at Asheville, N. C., and R. A.
St. George at Beltsville, indicates that DDT is very toxic to termites,
both as a soil poison and in treated wood. In the latter case, however,
it is of limited value because it has no fungicidal properties. Tests
with fiberboard are under way in the Tropics. Fabrics treated with 5-
percent solutions of DDT have been resistant to termite attacks, and
tests with lower concentrations are now being conducted. Fabrics treated
with DDT were severely damaged by mildew and decay.

Bark Beetles

DDT in an oil emulsion was tested by N. D. Wygant in the laboratory
for the prevention of attack by the Engelmann spruce beetle (Dendroctonus
engelmanni Hopk.) a bark beetle attacking living spruce trees in
Colorado. Preliminary results indicate that the beetles were prevented
from attacking green logs and finally all were killed.


Extensive experiments conducted by R. R. Whitten at the Morris-
town, N. J., laboratory with sprays containing DDT have given very
promising results in controlling the smaller European elm bark beetle
(Scolytus multlitriatus (Marsham)) the principal vector of the Dutch
elm disease pathogen. Various solutions and emulsions containing from
2 to 5 percent of DDT were effective in preventing crotch feeding in
living elm trees by adult beetles for more than 110 days. Lower con-
centrations of DIDT were effective for shorter periods. Similar sprays
containing as little as 0.25 percent of DIDT prevented beetles from
entering the bark of sprayed logs for over 69 days, and when the con-
centration of DDT was increased to 2 percent the period of protection
was extended to more than 160 days. An emulsion containing 0.5 percent
of DDI, when applied to elm wood infested with larval broods, permitted
some emergence of adults, but affected these emerging beetles to the
extent that none were able to attack suitable material caged with them.
Solutions of as little as 0.25 percent of DDT, when applied to similar
infested material, prevented all emergence.

Leafhoppers and Lygus

A number of preliminary cage and field tests were conducted at
the Columbus, Ohio, forest-insect laboratory by W. L. Baker and T. J.
Parr, with sucking insects, such as treehoppers and leafhoppers, sus-
pected of transmitting the virus that causes the elm phloem necrosis
disease. B. F. Anderson, at the Milwaukee, Wis., Laboratory, conducted
similar tests with the Saratoga spittle bug (Aphrophora saratogensis
(Fitch)), which causes a twig blight on pines in plantations in the
Lake States. Oil emulsions containing from 0.1 to 1 percent of DDT
were tested. Nearly all species readily succumbed to these dosages,
within 24 hours, indicating that these sprays may have much promise in
preventing such sucking insects from feeding. In the case of the spittle
bug, sprayed trees showed no sign of tip kill at the end of the season.
The material appeared to have a distinct repellent effect, but when the
insects were caged on sprayed branches complete mortality usually re-
sulted in 24 hours.

DDT has been found very effective against several insects affect-
ing the rubber-producing plant guayule. Lygus hesperus Knight, a
plant bug which has been notoriously hard to control on cotton and
other plants, succumbed readily to 2- to 5-percent DlDT dusts and to
emulsions containing from 0.15 to 0.3 percent of DDT. Mites were
readily controlled with emulsions of DDT.


Miscellaneous Forest Insects

Less extensive tests have been made on a considerable variety of
insects. For example, the eastern tent caterpillar (Malacosoma
americana (F.)) is effectively controlled by a very small amount of DDT
spray (such as 0.1 percent) applied as an emulsion to the egg bands or
later to the foliage or tents. The fall cankerworm (Alsophila pometaria
(Harr.)), the fall webworm (Hyphantria cunea Drury), the mimosa webworm
(Homadaula albizziae Clarke)), the bagworm ( Th2yrldopteryx ephemeraeformis
(Haw.)), the catalpa sphinx (Ceratomla catalpae (Bdv.)), and the boxwood
leaf miner (Monarthropalpus buxi Laboulb.) were all readily controlled
in small-scale tests with concentrations of 0.1 to 1 percent. The
abundance of black flies, mosquitoes, and deer flies was noticeably re-
duced in a number of sprayed plots, and high mortality occurred among
parasites. Adults of the locust borer (Cyllene roblniae (Forst.)) were
killed when DDT was applied as an emulsion either to the goldenrod on
which the beetles feed or to the stems of locust trees prior to ovi-
position. Preliminary tests indicate that a 1-percent DDT emulsion may
be used to control the white pine weevil (Pissodes strobi (Peck)), by
killing the adult beetles coming to the sprayed trees. J. E. Patterson
found it effective against the reproduction weevil (Cylindrocopturus
eatoni Buchanan)) In California. For the control of carpenter ants 17
log cabins in the Superior National Forest in Minnesota were sprayed by
H. C. Secrest with 1- and 5-percent solutions of DDT in kerosene.
Satisfactory control was obtained with a 5-percent solution.

In general, DDT has been used most effectively as a contact spray.
It is especially toxic to young larvae. There is considerable indication,
from work of S. F. Potts at New Haven, Conn., that it is also highly
toxic to mature larvae when used as a stomach poison in relatively low
dosages. As little as half a pound per acre gave good control of last
Instars of the gypsy moth on small hand-treated plots of low-growing

Effects of Solvents Used in Formulations

Laboratory tests during the present winter, conducted at Belts-
ville by R. A. St. George, C. H. Hoffmann, and others, and prompted by
results obtained from field applications made by R. R. Whltten during
the summer, indicate that the nature of the solvents used with DDT
has an extremely important bearing on toxicity. Some solvents, such
as kerosene, evaporate quickly (a matter of minutes) leaving slender,
needlelike crystals that are very durable, the toxic effects lasting
from 3 to 6 months wider outdoor weathering. These tiny crystals may
penetrate between the footpads of the insects and possibly enter the
pores in the eclerites of the body. Velsicol AR-50 (a mixture of mono-
and di-methylnaphthalene) produces similar crystals, but these require
a day or more to form. Heavy solvents, such as diesel oil, remain


tacky for days and leave a deposit that is not so persistent as that
resulting from kerosene. On the other hand, these tacky or viscous
films kill several times more quickly.

Relation of Insecticides to Silviculture

Forest entomologists have never been very enthusiastic about the
use of insecticides, because of cost and impracticability of applica-
tion. On the other hand, forest entomologists have repeatedly proposed
silvicultural recommendations as a means of preventing outbreaks of
forest insects. In a way such suggestions have been a bit before their
time, for actually there have been few satisfactory tests of these
suggestions. Many of them appear to have merit, and no doubt when it
becomes possible to test them on a large scale they will prove satis-
factory. Until economic conditions permit more intensive forest manage-
ment, the advent of DDT bids fair to bridge the gap with a fairly practi-
cal means of control. Nothing that can be said about the use of DDT at
present should be construed as obviating the need of encouraging every
practice that will make forest areas more resistant to insect outbreaks.

However, before DDT can be generally recommended for public use,
careful investigations must be conducted to determine the most effec-
tive and practical formulas for various uses, and its possible dele-
terious effect on man and domestic animals, beneficial insects, fish,
and wildlife. The expanding experimental programs should bring these
answers shortly.


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